1. Field of the Invention
The present invention relates to an apparatus for generating an independent coherent beam array from a single light source, and more particularly, to an apparatus for generating an independent coherent beam array in which beams are independently switched for recording and reading operations.
2. Description of the Related Art
FIG. 1 illustrates a conventional coherent beam array adapted in a holographic memory, which has been suggested in U.S. Pat. No. 4,988,153. In the coherent beam array, a plurality of vertical cavity surface emitting laser (VCSEL) diodes 14 form a two-dimensional laser diode array 12 as a light source. An XY selector 16 allows for selective electrical activation of a single or several VCSEL diodes in sequence.
The output beam from the selected VCSEL diode is converted into a collimated beam by a collimating lens 20. The position of the selected VCSEL diode, the X-Y coordinate of the selected VCSEL diode on the two-dimensional laser diode array 12, causes a small change in the incident angle of the collimated beam upon a holographic recording medium 10.
Images can be written to or read from the holographic recording medium 10 by collimated beams generated from the coherent beam array. During recording, an image 40 is presented on an image light source 42 and is recorded through a recording collimating lens 46 on the recording medium 10. The writing angle .theta..sub.W between the collimated beams respectively from the collimating lens 42 and the recording collimating lens 46, which are incident upon the recording medium 10, is varied, which allows multiple independent images to be superimposed and sequentially written to the recording medium 10. Although not illustrated, during reading, images recorded on the recording medium 10 are read out only by the collimated beam, of which the incident angle upon the recording medium 10 for reading is the same as that of the reference collimated beam.
The coherent beam array generating apparatus having the above-mentioned configuration can be applied to holographic information storing devices or displays, for optical interconnections therein, which require several tens to several hundreds of light sources. The manufacture of the VCSEL 12 is technically difficult, particularly in controlling the heat generated from laser diodes thereof and in maintaining the uniformity in the intensity of laser beams as well as irradiation angle of the laser beams, which increases the manufacturing cost and produces a low yield.